Milk lipase activity, initial concentration of free fatty acids (FFA) and free amino groups and subsequent lipolysis and proteolysis were measured in raw milk from cows fed either high (70%) or low (40%) amounts of concentrate. Lipase activity (2.36 µeq of FFA/ml/h) and initial FFA concentration (0.26 meq/100 g of fat) were higher in raw milk from cows fed high amounts of concentrate (2.04 µeq of FFA/ml/h AND 0.14 meq/100 g of fat respectively). Spontaneous lipolysis at 24 and 48 h was also higher in raw milk from cows fed high amounts of concentrate than in raw milk from cows fed low amounts of concentrate. Initial content of free amino groups (2.12 mmol/100 g of protein) and subsequent proteolysis at 48 h (2.28 mmol/100 g of protein) were higher (not significant) in raw milk from cows fed a high concentrate ration than those in raw milk from cows fed a low concentrate ration (1.99 and 2.14 mmol/100 g of protein, respectively). Some differences in lipolysis and proteolysis in raw milk were observed between weeks of treatment. Increased lipolysis and proteolysis products in raw milk from cows fed a diet high in concentrate may increase the rate of off-falvour appearance in milk and dairy products.